1. Field of the Invention
The present invention relates to an anti-seizing nut in which seizing scarcely occurs even when a bolt is screwed in an inclination direction.
2. Description of Related Art
In a case where a bolt is screwed into a nut, it is desirable to insert the bolt so that the axis of the bolt accurately matches the axis of the screw of the nut. However, in an actual automobile assembly line or the like, the bolt may be inserted into the nut while the axis is slightly inclined by the use of a tool such as a powered driver in some cases. In this case, a thread ridge of the bolt is fitted to a groove deviated by one pitch from the fitting target groove of the screw of the nut. In this state, when the bolt is forcedly threaded into the nut, seizing occurs, and hence a severe trouble may occur in which the bolt is not easily separated from the nut.
Therefore, various bolts have been proposed which prevent the seizing even when the bolt is obliquely inserted into the nut. As a representative example, according to Patent Document 1 of the present applicant, a front end of a nominal female-threaded portion is provided with a pilot portion (called a bar tip portion or a guide portion), and an outer periphery of a front end of the pilot portion contacts the screw when a bolt is inserted in the inclination direction, thereby correcting the posture of the bolt. Further, as illustrated in Patent Document 2 and Patent Document 3, an anti-seizing bolt is also proposed which improves a posture correction effect by forming various thread ridges in a pilot portion.
Incidentally, since the diameter of the pilot portion is, of course, smaller than that of the nominal female-threaded portion of the bolt, a small-diameter female-threaded portion is inevitably formed between the nominal female-threaded portion and the pilot portion, and hence seizing occurs in the small-diameter female-threaded portion. Further, even when the pilot portion is formed in a long size, no particular seizing preventing effect is exhibited just by decreasing the inclination of the bolt. Moreover, the pilot portion becomes a useless portion that does not contribute to the improvement in fastening force in the fastened state. For this reason, it is not an advantageous countermeasure to form the long pilot portion even from the viewpoint of costs and resources.
Furthermore, Patent Document 4 discloses a technique of preventing seizing by cutting out the thread ridge end portions of the nut and the bolt so as to remove an incomplete female-threaded portion. However, in this technique, both the bolt and the nut are formed in a particular shape, and hence only one of them may not be used solely. In this way, the related art on the nut that prevents the seizing even when the bolt having a general shape is obliquely inserted into the nut substantially does not exist.
Patent Document 1: JP 10-141343 A
Patent Document 2: JP 3336257 B2
Patent Document 3: WO 2006/134626
Patent Document 4: JP 10-274227 A